The present invention relates to an ink jet system printer of the charge amplitude controlling type and, more particularly, to a droplet charge condition detection system in an ink jet system printer of the charge amplitude controlling type.
An ink jet system printer of the charge amplitude controlling type includes an ink droplet issuance unit to which an electromechanical transducer is attached to vibrate the ink droplet issuance unit at a given frequency, thereby forming the ink droplet at the given frequency. The ink droplet is charged by a charging tunnel in accordance with a print data, and the thus charged ink droplet is deflected in accordance with the charge amount carried thereon while it passes through a constant high voltage deflection field established by a pair of deflection electrodes. The thus deflected ink droplet is directed to a recording paper to print a desired pattern in a dot matrix fashion.
In such an ink jet system printer of the charge amplitude controlling type it is strictly required that the application of the charging signal is timed in agreement with the droplet formation timing. If the charging signal application is not synchronized with the droplet formation, an accurate printing can not be ensured. Further, the droplet formation timing is variable depending on the ambience condition even when the ink jet system printer continuously operates. Therefore, a system is required to determine whether the application of the charging signal is timed in agreement with the droplet formation timing.
It is conventional in an ink jet system printer of the charge amplitude controlling type that phase detecting dots are provided in addition to the ink droplets contributing to the actual printing operation in order to detect whether the ink droplets are properly charged by the charging signal. To detect the charge condition of the phase detecting dots, the conventional ink jet system printer includes a charge amplitude detection electrode disposed at the downstream of the charging tunnel for detecting the charge voltage through the use of the electrostatic induction. A typical construction of the charge amplitude detection electrode is disclosed in U.S. Pat. No. 3,953,860, Charge Amplitude Detection for Ink Jet System Printer, issued on Apr. 27, 1976. Such a detection system is not practical because it is very difficult to maintain the charge amplitude detection electrode at a high impedance condition.
A novel charge condition detection system is proposed in copending application Ser. No. 917,592, Phase Detection in an Ink Jet System Printer of the Charge Amplitude Controlling Type, filed on June 21, 1978 by Masahiko Aiba and Ikuo Umeda and assigned to the same assignee as the present application, now U.S. Pat. No. 4,288,796 issued Sept. 8, 1981, wherein a detection system is provided for detecting an electric current which will flow from the nozzle to the ink liquid when application of a phase detection signal to a charging tunnel is timed in agreement with a droplet formation phase. More specifically, a resistor is connected to the nozzle, and the detection system is connected to the resistor for detecting a voltage across the resistor which is representative of the above-mentioned electric current. The detection system disclosed in Ser. No. 917,592 is not practical because the detection output includes large level noises.
An improvement over the detection system disclosed in Ser. No. 917,592 is proposed in copending application Ser. No. 124,850, Charge Timing Evaluation in an Ink Jet System Printer of the Charge Amplitude Controlling Type, filed on Feb. 26, 1980 by Masahiko Aiba and assigned to the same assignee as the present application now U.S. Pat. No. 4,329,695 issued May 11, 1982. In the detection system disclosed in Ser. No. 124,850, an alternating current signal is obtained from the electric current flowing from the nozzle to the ink liquid when the ink droplets are properly charged by the charging tunnel. However, the alternating current signal includes a large amount of noise component.
Accordingly, an object of the present invention is to provide a charge condition detection system in an ink jet system printer of the charge amplitude controlling type.
Another object of the present invention is to provide a charge current detection system which develops a detection output of a high S/N ratio.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a detection electrode is disposed in an ink liquid supply system to contact the ink liquid. A capacitor is connected to the detection electrode so that the capacitor accumulates charges corresponding to the charges applied to the ink droplets by a sequence of phase detection charging signals. A detection circuit is connected to the capacitor to remove the noise component, thereby obtaining a D.C. detection signal. In a preferred form, the detection circuit includes a low-pass filter for removing the noise component.